Method of comminuting wood for making carbons



Patented Sept. 20, 1938 METHOD OF COMMINUTING WOOD FOR MAKING CARBONS Richard w. Schmidt, Redondo Beach, Calif., as signor to The Evanston Company, Los Angeles, Calif., a corporation of Nevada No Drawing. Application January 16, 1937, Serial No. 121,015

5 Claims.

In a copending application filed February 19, 1935 under Serial No. 7,261 and entitled Decolorizing and filtering agent I havedescribed a process in which a powerful decolorizing agent having a a high filtering value is produced by carbonizing a mixture of wood flour and diatomaceous earth and activating the product by contact with a mild gaseous oxidizing agent.

In the copending application it is disclosed that the best results are obtained when the wood is subdivided to a very considerable degree, for example to such fineness as will substantially entirely pass through a standard 70-mesh screen, this fine subdivision of the wood permitting it to be intimately dispersed throughout the.mass of diatomaceous earth and permitting the vapors evolved in the carbonization to pass immediately into contact with earth particles on which layers of active carbon are formed.

In putting the invention of the copending disclosure into practical application I encountered the difiiculty that sawdust and similar waste wood products contain as a rule a very small proportion of particles which will pass through a 70-mesh screen, the quantities so obtainable being too small to be of any commercial importance. On the other hand sawdust, shavings, slabs, and various trimmings from the man ufacture of lumber and other wood products may be had in enormous quantity and at a negligible cost, but the expense incident to reducing these products to anything approaching a 70-mesh fineness constitutes a very heavy burden because of the toughness and resilience of small wood fragments and their consequent resistance to fine comminution, which can be overcome only by passing them through large hammer mills operated at a high speed and consuming very large amounts of power as offset against a very limited output.

I have discovered that this difl'lculty may be entirely overcome without detriment to any succeeding step by first subjecting the wood fragments, of whatever form and size, to a preliminary drying operation carried to a temperature falling short of that of carbonization. In this operation time and temperature are to some degree interchangeable but the final temperature to which the wood is subjected should in any case be above 250 F. and the application of this temperature, or of a higher one, should be continued until the wood takes on a deep yellow or pale brownish color. The operation may be accelerated by increasing the temperature though it is seldom necessary or desirable to go above 500 F.

The time required will obviously vary materially with the size of the fragments, for example coarse sawdust such as that yielded by slabbing saws acquires the desired consistency within a minute or two at a temperature of say 450 F., while 5 slabs and larger cuttings require the greater time necessary for the penetration of heat to the center of the largest piece.

Wood which has been treated in this manner will be found to have had its toughness and resilience destroyed to such an extent that it may ordinarily be rubbed to a powder between the fingers. Because of this high degree of friabllity, it may be reduced to a powder of any desired mesh by passing between light crushing rolls or 15 through a roller or hammer mill, either of these operations giving a very large yield with an insignificant consumption of power.

I have made numerous experiments in which the process of the copending application has been 20 applied to wood thus prepared and, under identical conditions, to wood which has been comminuted without the application of this predrying step. The results from these comparative tests were indistinguishable and the predrying step 25 appears to have no deleterious effect whatever on the quality of the final activated product.

The wood powders produced in this manner have numerous uses other than that above described, and may advantageously be substituted 30 for the wood flour of commerce in many operations and compositions. For example, they may be used in compositions such as the so-cailed wood-stone, in which they are mixed with a binding or cementing agent to form light weight 35 slabs and shapes, and in high temperature insulating compounds in which they serve as temporary binders. The product is also useful in the manufacture of porous ceramic products in which manufacture it is burned out during the 40 firing step, producing pores and vesicles in the finished ware. For such uses these products are markedly superior to wood flour prepared in the ordinary manner (by grinding green or kiln dried wood or by screening sawdust) because of 45 the greater length of the fibre, the powder prepared by grinding or crushingpreviously heated wood consisting in large part of needle-like fibres of considerable length.

For the first purpose named-the preparation 50 of a decolorizing and filtering agent-the color and odor of the product are unimportant, and it I is usually desirable and never detrimental to hasten the operation by working in the upper range of temperature, as of the order of 450 to erated at relatively 500' Fahr. But for other uses the dark color (which is permanent) and the scorched odor (which disappears in a short time after grinding), of the product prepared. at these temperatures, may be. objectionable. For such uses, therefore, it may be desirable to work in the lower range of temperature, as for example from 250 to 350 Fahr., correspondingly lengthening the period of heating to ensure destruction or desiccation of the resins and other substances by which the cellulosic fibres of the original wood are bound together. Thefibres may thus be liblow temperatures with very little darkening and without the development of any objectionable odor, but the minimum temperature at which this result may be attained is that which produces substantially complete dehydration of the wood and cannot be materially below 250 Fahr. Down to this temperature, however, the sole objectionable feature of a lowering of temperature is the extension of the heating time thus occasioned.

I claim as my invention:

1. In a method of manufacturing a decolorizing and filtering material which comprises carbonization of a mixture of woody material and diatomaceous earth and the activation of the carbonized product, the preliminary steps of heating said woody material to a temperature at which said woody material is appreciably darkened in color; continuing said heating until said woody material is rendered readly friable; discontinuing said heating before material carbonization of said woody material takes place, and reducing the heat treated woody material to powdered condition for admixture with said earth.

2. The method of manufacturing a pulverized wood carbon which comprises: heat treating the wood under such conditions of time and temperature as to render the wood readily friable while preserving itsidentity as wood; pulverizing the heat treated wood only after the completion of said heat treatment. and thereafter carbcnizing the pulverized wood.

3. The process of preparing comminuted woody material adapted for use in the manufacture of decolorizing carbons which comprises a preliminary step of heat treating the wood at a temperature above that required for its complete desiccation and at which the color of said wood is appreciably darkened, said temperature being below that at which material carbonization of said wood takes place, said heat treatment being applied immediately and only prior to the comminuting operation.

4. In a method of manufacturing a decolorizing and filtering material involving the carbonization of a mixture of wood and diatomaceous earth: the preliminary steps of heat treating said wood at a temperature in excess of that required for complete drying and sufficient to render said wood more fragile than when only completely dried, said temperature being below that at which material carbonization occurs; of finely comminuting said heat treated wood, and of avoiding the presence of any water-containing substance during said comminuting step.

5. The method of preparing a finely comminuted wood product with includes the followin steps in the order stated: heat treating said wood for a time and at a temperature in excess of the time and temperature required for complete drying of said wood and thereby rendering said wood more fragile than said wood when only completely dried; interrupting said heat treatment before material carbonization of said wood occurs, and comminuting said heat treated wood only after the completion of said heat treating step.

RICHARD W. SCHMIDT. 

